It is well known that substantial muffling of internal combustion engines is necessary in order to reduce objectionable noise. However, it is desirable to reduce the level of exhaust noise without seriously interfering with exhaust outflow. A large variety of mufflers have been developed to meet these twin objectives for internal combustion engines.
In some environments where internal combustion engines are used, it is mandatory that the emissions of glowing carbon particles from the exhaust be prevented so as to avoid fires in the surrounding environment. This is particularly true in applications such as off-road motorcycles or xe2x80x9cdirt bikesxe2x80x9d. A spark arresting muffler capable of catching and retaining sparks of carbon and the like discharged by the engine is necessary in such an environment because any sparks which might otherwise escape to the surroundings pose a fire hazard. Various arrangements have been provided for this purpose. One such design is shown in U.S. Pat. No. 3,987,867, issued on Oct. 26, 1976. Another such design is illustrated in U.S. Pat. No. 4,113,051, which issued on Sep. 12, 1978. Both of these patents are owned by the assignee of the instant application.
The known muffler and spark arrester designs have an enclosure including a perforated inner tube which is coaxially located within an outer tube. A sound absorbent material is placed between the tubes. At the outlet end of the inner and outer tubes, there is provided a gas barrier wall with a partially toroidal concave configuration. Against this wall nests a plurality of partially toroidal circular discs slightly spaced apart by edge dimples.
Another known engine muffler and spark arrester includes an oval shaped outer tube which is coupled to a plurality of substantially identical nested oval shaped discs. This design is illustrated in U.S. Pat. No. 5,869,793, dated Feb. 9, 1999 and also owned by the assignee of the instant application. All three of these patents are incorporated into this specification by reference in their entireties.
All three of the muffler designs illustrated in the patents referenced above, as well as a variety of competitive products, are so configured that the exhaust gases from the internal combustion engine to which the mufflers are fluidly connected exit radially around the outside diameters of the discs. However, such an exhaust path does not meet certain government noise regulations which limit the exhaust angle. More particularly, the Japanese Ministry of Transportation has a standard which requires that the exhaust from the muffler must exit within 30xc2x0 of the centerline of a motor vehicle. Even decreasing the exhaust angle at the outer edges of the known discs will not necessarily comply with this standard due to the angle at which the muffler may be mounted on the motorcycle or other vehicle in relation to the longitudinal axis of the vehicle.
Accordingly, it has been considered desirable to develop a new and improved muffler system which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.
In accordance with one aspect of the present invention, an engine muffler and spark arrester is provided.
More particularly, in accordance with this aspect of the invention, the muffler comprises an outer tube extending along an axis and having an outlet end. A plurality of substantially identical nested discs is disposed coaxially adjacent the outlet end of the outer tube. Each of the discs has at least one slot extending therethrough. The at least one slot of each of the plurality of discs allows an approximately axial exit of at least a portion of the exhaust outflow of an associated engine to which the muffler is connected.
In accordance with another aspect of the present invention, a tunable engine muffler is provided.
More particularly, in accordance with this aspect of the invention, the muffler comprises an outer tube extending along an axis and having an outlet end. An outlet cap is secured to the outlet end of the outer tube. The outlet cap has a centrally located aperture extending therethrough. A plurality of substantially identical nested discs are disposed coaxially adjacent the outlet cap. A first of the plurality of discs is located adjacent the outlet cap. An end cap is located adjacent a last of the plurality of discs. The end cap and the plurality of discs each include at least one slot through which at least a portion of the exhaust gases from an internal combustion engine to which the muffler is connected can flow in an approximately axial direction which is offset from an axial center line of the muffler.